Ultrafiltration membranes have been employed extensively in the separation and concentration of electrophoretic aqueous paint compositions, particularly for use in the automotive field. The concentration and/or separation of cathodic electrophoretic paint compositions, through the use of ultrafiltration membranes, has been accompanied with many problems, due to the nature of the cathodic electrophoretic paint compositions employed. Typically the ultrafiltration membranes employed in such separation and concentration process have been subject to extensive and massive membrane fouling, leading to a rapid diminution in the flux of the membranes. Therefore, specific, special ultrafiltration membranes have been developed for specific cathodic electrophoretic paint compositions.
It has been found, for example, that ultrafiltration membranes, having fixed positive charges, are more immune to membrane fouling in the separation and concentration of cathodic electrophoretic paints than ultrafiltration membranes which do not have fixed positive charges. Typical ultrafiltration membranes in use, having fixed positive charges, generally contain positive-charged nitrogen atoms, such as membranes made from copolymers of acrylonitrile and an ionogenic comonomer. Such ultrafiltration membranes have not proven to be wholly satisfactory, and, therefore, there exists a need for the development of an ultrafiltration membrane particularly adapted to separate and concentrate cathodic electrophoretic paints without massive fouling, and which membrane has a long use life at high flux rates.